arXiv subjects
Publications and source records attributed to Stanislaw Mrowczynski.
We study the collective quark excitations in an extremely anisotropic system of two interpenetrating streams of the quark-gluon plasma. In contrast to the gluon modes, all quark ones appear to be stable in such a system. Even more, the quark modes in the two-stream system are very similar to those in the isotropic plasma.
The event-by-event p_T-fluctuations in proton-proton and central Pb-Pb collisions, which have been experimentally studied by means of the so-called Phi-measure, are analyzed. The contribution due to the correlation which couples the average p_T to the event multiplicity is computed. The correlation appears to be far too weak to explain the preliminary experimental value of Phi (p_T) in p-p interactions. The significance of the result is discussed.
Charge fluctuations studied on event-by-event basis have been recently suggested to provide a signal of the equilibrium quark-gluon plasma produced in heavy-ion collisions at high energies. It is argued that the fluctuations generated at the early collision stage when the energy is released can fake the signal.
Using a microscopic phase-space model of the membrane system, the boundary condition at a membrane is derived. According to the condition, the substance flow across the membrane is proportional to the difference of the substance concentrations at the opposite membrane surfaces. The Green's function of the diffusion equation is found for the derived boundary condition and the exact solution of the equation is given.
Anisotropic systems of quarks and gluons, which at least for sufficiently short space-time intervals can be treated as homogeneous and static, are considered. The gluon polarization tensor of such a system is explicitly computed within the semiclassical kinetic and Hard Loop diagrammatic theories. The equivalence of the two approaches is demonstrated. The quark self energy is computed as well, and finally, the dispersion relations of quarks and gluons in the anisotropic medium are discussed.
The event-by-event azimuthal fluctuations in high-energy heavy-ion collisions are analyzed by means of the so-called Phi-measure. The fluctuations due to the collective transverse flow and those caused by the quantum statistics and resonance decays in the hadron gas are discussed in detail.
The Phi-measure of event-by-event fluctuations in high-energy heavy-ion collisions corresponds to the second moment of the fluctuating quantity distribution of interest. It is shown that the measure based on the third moment preserves the properties of Phi but those related to the higher moments do not. In particular, only the second and third moment measures are intensive as thermodynamic quantities. The Phi_2- and Phi_3-measure of p_T-fluctuations are computed for the hadron gas in equilibrium and the results are analyzed in context of the experimental data.
An elementary introduction to the physics of quark-gluon plasma is given. We start with a sketchy presentation of the Quantum Chromodynamics which is the fundamental theory of strong interactions. The structure of hadrons built up of quarks and gluons is briefly discussed with a special emphasis on the confinement hypothesis. Then, we explain what is the quark-gluon plasma and consider why and when the hadrons can dissolve liberating the quarks and gluons. The heavy-ion collisions at high-energies, which provide a unique opportunity to get a droplet of the quark-gluon plasma in the terrestrial conditions, are described. We also consider the most promising experimental signatures of the quark-gluon plasma produced in nucleus-nucleus collisions. At the end, the perspectives of the quark-gluon plasma studies at the future accelerators are mentioned.
Fluctuations of the chemical composition of the hadronic system produced in nuclear collisions are discussed using the $Φ-$measure which has been earlier applied to study the transverse momentum fluctuations. The measure is expressed through the moments of the multiplicity distribution and then the properties of $Φ$ are discussed within a few models of multiparticle production. A special attention is paid to the fluctuations in the equilibrium ideal quantum gas. The system of kaons and pions, which is particularly interesting from the experimental point of view, is discussed in detail.
The so-called $Φ$ parameter, which measures the transverse momentum or energy correlations (fluctuations) in high-energy collisions independently of the particle multiplicity, is computed for the equilibrium ideal gas. As expected $Φ$ vanishes for the particles obeying Boltzmann statistics but is finite for the quantum particles, positive for bosons and negative for fermions. $Φ_{p_{\perp}}$, which is found for the pions gas, significantly exceeds the value of $Φ_{p_{\perp}}$ measured by the NA49 experiment. The discrepancy is discussed.
The near membrane layer is defined as a region where the concentration of the substance transported across the membrane drops $k$ times. The time evolution of such a layer is studied experimentally by means of the laser interferometric method. It is shown that within the experimental errors the thickness of the near membrane layer grows in time as $a \sqrt t$ with the coefficient $a$ being independent of the initial concentration and the membrane permeability. Time evolution of the near membrane layers is also analyzed within the theoretical approach earlier developed by one of us. The regularities found experimentally fully agree with the theoretical expectations.
The calculations of the elementary atom (the Coulomb bound state of elementary particles) interaction with the atom of matter, which are performed in the Born approximation, are reviewed. We first discuss the nonrelativistic approach and then its relativistic generalization. The cross section of the elementary atom excitation and ionization as well as the total cross section are considered. A specific selection rule, which applies for the atom formed as positronium by particle-antiparticle pair, is analyzed.
We propose a method to measure the hadronic matter compressibility by means of the event-by-event analysis of heavy-ion collisions at high energies. The method, which utilizes the thermodynamical relation between the compressibility and the particle number fluctuations, requires a simultaneous measurement of the particle source size, temperature and particle multiplicity.
A few topics of the transport theory of quark-gluon plasma are reviewed. A derivation of the transport equations form the underlaying dynamical theory is discussed within the $ϕ^4$ model. Peculiarities of the kinetic equations of quarks and gluons are considered and the plasma (linear) response to the color field is studied. The chromoelectric tensor permeability is found and the plasma oscillations are discussed. Finally, the filamentation instability in the strongly anisotropic parton system from ultrarelativistic heavy-ion collisions is discussed in detail.
The pion multiplicity per participating nucleon in central nucleus-nucleus collisions at the energies 2-15 A GeV is significantly smaller than in nucleon-nucleon interactions at the same collision energy. This effect of pion suppression is argued to appear due to the evolution of the system produced at the early stage of heavy-ion collisions towards a local thermodynamic equilibrium and further isentropic expansion.
Using the kinetic theory we discuss how the particle and energy densities of the quark-gluon plasma fluctuate in a space-time cell. The fluctuations in the equilibrium plasma and in that one from the early stage of ultrarelativistic heavy-ion collisions are estimated. Within the physically interesting values of the parameters involved the fluctuations appear sizeable in both cases.
Using the Schwinger-Keldysh technique we discuss how to derive the transport equations for the system of massless quantum fields. We analyse the scalar field models with quartic and cubic interaction terms. In the $ϕ^4$ model the massive quasiparticles appear due to the self-interaction of massless bare fields. Therefore, the derivation of the transport equations strongly resembles that one of the massive fields, but the subset of diagrams which provide the quasiparticle mass has to be resummed. The kinetic equation for the finite width quasiparticles is found, where, except the mean-field and collision terms, there are terms which are absent in the standard Boltzmann equation. The structure of these terms is discussed. In the massless $ϕ^3$ model the massive quasiparticles do not emerge and presumably there is no transport theory corresponding to this model. It is not surprising since the $ϕ^3$ model is anyhow ill defined.
We study color fluctuations in the quark-gluon plasma produced at the early stage of nucleus-nucleus collision at RHIC or LHC. The fluctuating color current, which flows along the beam, can be very {\it large} due to the strong anisotropy of the parton momentum distribution. A specific fluctuation, which splits the parton system into the current filaments parallel to the beam direction, is argued to grow exponentially. The physical mechanism responsible for the phenomenon, which is known as a filamentation instability, is discussed.